Watermelon is an important specialty crop that is common in all major agriculture production areas and accounts for 2% of the world area devoted to vegetable crops. There were 3,743,497 of hectares of watermelon grown in the world and 55,200 hectares of watermelons grown in the United States in 2006. Asia is by far the most important watermelon production site with nearly ⅔ of the world area and slightly over ⅔ of the world production (United Nations, Food and Agriculture Organization, FAOStat (2/2008)). There were 64,840 hectares of watermelon planted in the USA with a total production of 42,869,000 cwt and farm value of $476,209,000 in 2007 (USDA, NASS, Vegetables Annual Summary (1950-81 and 1992-2007)). California was the leading state in watermelon farm gate value, exceeded $72 million in 2000, due to high percentage of triploid seedless watermelon grown in California. Seedless watermelon receives well above the average price for seeded watermelons in the market. Triploid seedless watermelon also produces higher yields than the diploid seeded watermelons. The significantly increased watermelon productivity and farm value, as well as decreased production acreage, in the USA since the mid-1990s are the result of using triploid seedless watermelon varieties in commercial production.
As with many different plants, watermelon contains a fruit part and a plant part. Each part contains different traits that are desired by consumers and/or growers, including such traits as flavor, texture, disease resistance, and appearance traits such as shape and color. The seedless trait in the watermelon fruit is highly desired by consumers. For production of seedless watermelon, optimum pollination characteristics of the pollenizing plant are desired.
Seedless watermelon plants are triploid and must be pollinated by the pollen of seeded watermelon plants. To provide adequate pollenization of seedless watermelon plants, the recent practice has been to plant pollenizer plants over approximately 25-33% of the field surface. The remaining portion of the field is planted with the triploid seedless watermelon plants. Thus, to maximize the value of the crop in the field, growers used high yield marketable diploid watermelon varieties as pollenizers. These pollenizers ultimately competed with the triploid seedless varieties for sun, nutrients, space, and are also more susceptible to foliar diseases. Diploid seeded varieties mature earlier than triploid seedless varieties, thus requiring harvesting prior to the seedless varieties reaching maturity.
However, the seedless watermelon industry went through a revolutionary change in production practices in 2001 when Syngenta Seeds, Inc. released its enhanced diploid non-harvestable watermelon pollenizer, referred to as “Super Pollenizer”, or SP-1. This enhanced watermelon pollenizer is protected by U.S. Pat. No. 6,759,576. (See also U.S. Pat. No. 7,071,374.) This innovative variety employed a novel diploid, non-competitive watermelon plant to improve upon current methods of commercial production of seedless watermelons, increasing the number of triploid seedless plants per acre and thereby increasing seedless watermelon yields per acre. Since that time, other enhanced watermelon pollenizers have come into the market place.
Enhanced watermelon pollenizers like SP-1 have small leaves that allow the pollenizer to be grown in close proximity to the triploid seedless watermelon plants without competing with them, thereby increasing seedless plant populations and yields of seedless fruits. The enhanced watermelon pollenizer has leaves that take up less field area than the substantially larger leaves of the pollenizers used in the past for production of seedless watermelon. Thus, as it is less competitive for light, water and fertilizers, enhanced watermelon pollenizers are grown closer to the triploid watermelon plants, and do not need dedicated space to grow. When enhanced pollenizers are used, the triploid seedless watermelon plants are typically grown in solid rows at a standard spacing, the enhanced watermelon pollenizer being then inter-planted between the plants within the rows. The result is a significantly higher number of triploid watermelon plants per acre compared to the number of triploid watermelon plants that has traditionally been planted, and higher yields of seedless fruits.
Due to germination issues with triploid watermelon seeds, triploid watermelon plants are normally sold as young plants and not as seeds. Because of this, enhanced watermelon pollenizers are often sold as transplants along with the triploid watermelon plants. As an example, Syngenta sells transplants through a transplant business that provides the enhanced watermelon pollenizer SP-1 along with a triploid seedless watermelon variety, both in the form of transplants, or so-called young plants.
The watermelon transplants are produced by commercial vegetable greenhouses located in the regional watermelon production areas to allow for delivery to the grower's field. The commercial greenhouses obtain seed either from growers or suppliers. These transplant producers grow the young plants to meet specific transplanting dates in the field.
Watermelon plants are produced in 30 to 50 cm3 “cell” trays containing a soilless soil mix of 50 to 65% high grade peat and 35 to 50% horticultural vermiculite or horticultural perlite. Some common trays used in watermelon transplanting range from 98, 128, 200 and 242 cells per tray and are composed of various materials such as hard Styrofoam, hard plastic or flexible plastic materials.
Watermelons are placed one seed per cell and sown about 2-cm deep. The planting media is generally pre-watered lightly prior to seeding to bring the seed and mix in contact. Trays are then placed under controlled humidity and temperature for 24-48 hours by covering and placing in a germination chamber at 30-35 C. The trays are then arranged on benches in a greenhouse with day temperature 21-27 C and night temperature 18-21 C where temperature control can be achieved.
Plants are grown in the greenhouses and ready for transplanting when the roots are sufficiently developed to permit removal from the cell with the entire growing mix volume intact. This will generally require four to six weeks from sowing or seeding, depending on cell size, light and temperature conditions.
Current seeding methods include semi-automated equipment and hand sowing techniques. The largest percentage of commercial watermelon transplant producers use mechanical seeders that are typically based on vacuum technology for precision placement of the seed in the tray cells. The automated process involves filling the trays with planting media which is then moved under a “punch or dibble” allowing for the proper depth and insures positioning of the seed in the center of the cell.
There are a number of manufacturers, styles and engineering designs of commercial semi-automated seeders used in the industry. These seeders utilize different technologies, such as air vacuum to pick up the seed and releasing the seed into the tray cell by releasing the seed by air or water pressure.
The current commercial method and process for delivering transplants to watermelon growers includes that the triploid seedless watermelon seeds and the enhanced watermelon pollenizer seeds are grown in separate trays while in the greenhouse. This is considered necessary due to the cultural practices required in the greenhouse to produce healthy and usable seedling plants for transplanting. Prior to the introduction of SP-1 by Syngenta, the diploid seeded watermelon pollenizers then in use would compete for light and space within the tray, thwarting the growth of the triploid seedless watermelon plants. In addition, the number of growing days and nutritional requirements to produce a usable transplant is different for the triploid watermelon plants and the diploid seeded pollenizers. For this reason, all pollenizers continue to be seeded in trays dedicated to the varieties and placed in the greenhouse separate from the seedless varieties and tray as this has always been the common practice.
In the field, watermelon pollenizers are planted in different ratios when planted with the triploid seedless watermelons to ensure that viable pollen is available for the production of the seedless fruit. These ratios widely differ based on the varieties used, the number of plants per acre, plant distance down the row and square feet occupied per plant bed widths, as well as environmental factors during field production. They can be in ratios of 1 seedless plant to 1 pollenizer plant (1:1 ratio) and at times up to 5 seedless plants to 1 pollinator plant (5:1 ratio). The most commonly used ratios are 2:1, 3:1 and 4:1 seedless to seeded pollinator ratios.
These ratios of pollenizers planted greatly affect the commercial greenhouse producer's profitability and efficiencies in transplant production. The trays dedicated to pollenizers take up valuable space in the greenhouse and require different cultural practices within the greenhouse in terms of irrigation and fertility management due to differences in the number of growing days and sowing dates between the seedless and pollenizer varieties. Logistics is also compromised when placing and tagging the pollenizer trays to separate them from the seedless trays in the greenhouse. Pollenizer trays will occupy 20%-50 of the greenhouse space, compromising seedless quantities and assuming a large % of the freight costs.
Commercial greenhouse producers make arrangements with growers for delivery of triploid seedless and pollenizers at specific dates. Most commonly, the watermelon transplants are loaded and placed in racked trailers or boxes for delivery directly to the field location. This involves organized and well managed hand labor to ensure that the triploid seedless trays and seeded pollenizer trays are clearly separated and marked prior to and during the loading operation destined for the grower's field.
Not only are greenhouse logistical costs compromised utilizing the current process and methods but freight and shipping costs are affected due to the space required in the trailer or container for the pollenizer trays. Due to increasing fuel costs associated with delivery of the trays to the field, it is estimated that for every acre of seedless plants delivered to the grower, the additional weight for pollenizers is 50 lbs on the trailer or container. This includes the weight of the tray, and the moist planting media. In addition, for every acre of seedless delivered, pollenizer trays occupy an estimated 14 cubic feet of valuable and expensive space within the trailer or container.
Commercially, watermelon transplants are planted in fields by mechanical transplanting machines, hand labor or a combination of both methods. The pollenizer plant must be planted and placed in the field occupying a dedicated space and at the correct ratio and dispersion in the field to ensure that pollen can be easily transferred utilizing bees to the seedless plants and female flowers to produce the seedless fruit. For mechanical transplanting, this involves specialized equipment setup and a dedicated laborer or effort dedicated to the placement of the pollenizer transplant in the correct position in the field. When using hand labor for transplanting, it involves additional labor and the separation of the crews to ensure the correct ratios are placed in the field.
The introduction to the industry of the SP-1 enhanced watermelon pollenizers provided a unique planting sequence in the field that further complicated field transplanting methods and logistics for the grower. SP-1 and other enhanced watermelon pollenizers do not compete with triploid seedless watermelon varieties for light, space or nutrition. This enabled growers to plant enhanced watermelon pollenizers in a non-dedicated space, i.e., interspersed within the same part of the field as the triploid seedless variety. This change created logistics problems in the field and increased costs associated with the transplantation of watermelon seedlings to the field. For example, transplanting by hand labor requires additional costs associated with the dedicated labor to transplant the enhanced watermelon pollenizer plants in between the seedless plants. This additional cost to the growers is an estimated $50-$60 per acre of seedless watermelons for transplanting enhanced watermelon pollenizers.